body {
font-family: -apple-system, BlinkMacSystemFont, "Segoe UI", Roboto, Helvetica, Arial, sans-serif;
line-height: 1.6;
color: #333;
max-width: 800px;
margin: 0 auto;
padding: 20px;
background-color: #f9f9f9;
}
.calculator-container {
background: #ffffff;
border: 1px solid #e0e0e0;
border-radius: 8px;
padding: 30px;
box-shadow: 0 4px 6px rgba(0,0,0,0.05);
margin-bottom: 40px;
}
.calculator-title {
margin-top: 0;
margin-bottom: 20px;
color: #2c3e50;
text-align: center;
}
.input-group {
margin-bottom: 20px;
}
.input-group label {
display: block;
margin-bottom: 8px;
font-weight: 600;
color: #555;
}
.input-group input {
width: 100%;
padding: 12px;
border: 1px solid #ccc;
border-radius: 4px;
font-size: 16px;
box-sizing: border-box;
}
.input-hint {
font-size: 12px;
color: #777;
margin-top: 4px;
}
.calc-btn {
display: block;
width: 100%;
background-color: #007bff;
color: white;
border: none;
padding: 15px;
font-size: 18px;
font-weight: bold;
border-radius: 4px;
cursor: pointer;
transition: background-color 0.2s;
}
.calc-btn:hover {
background-color: #0056b3;
}
.result-box {
margin-top: 25px;
background-color: #f1f8ff;
border: 1px solid #cce5ff;
border-radius: 4px;
padding: 20px;
display: none;
}
.result-box h3 {
margin-top: 0;
color: #004085;
}
.result-value {
font-size: 2em;
font-weight: bold;
color: #0056b3;
margin: 10px 0;
}
.result-detail {
margin-bottom: 10px;
font-size: 14px;
color: #555;
}
.article-content h2 {
color: #2c3e50;
border-bottom: 2px solid #eee;
padding-bottom: 10px;
margin-top: 40px;
}
.article-content p {
margin-bottom: 15px;
}
.article-content ul {
margin-bottom: 15px;
padding-left: 20px;
}
.highlight-box {
background-color: #fff3cd;
border: 1px solid #ffeeba;
padding: 15px;
border-radius: 4px;
margin: 20px 0;
}
How to Calculate Pipe Size Based on Flow Rate
Correctly sizing a pipe is a fundamental step in fluid dynamics and plumbing engineering. The size of the pipe determines the velocity of the fluid for a given flow rate. If a pipe is too small, the fluid velocity increases, leading to excessive pressure drop, noise, potential erosion, and higher energy costs for pumping. Conversely, if a pipe is too large, it may lead to sedimentation issues and unnecessary material costs.
The Core Formula
The relationship between pipe diameter, flow rate, and velocity is derived from the continuity equation:
Q = A × v
- Q = Flow Rate (e.g., cubic feet per second or GPM)
- A = Cross-sectional Area of the pipe
- v = Velocity of the fluid
Solving for Diameter
Since pipes are circular, the Area (A) is calculated using the diameter (d): A = π × (d/2)² or A = (π × d²) / 4.
To find the required diameter based on a known Flow Rate (Q) and a target Velocity (v), we rearrange the formula:
d = √ [ (4 × Q) / (π × v) ]
Practical Example
Let's say you have a system requiring a flow rate of 100 Gallons Per Minute (GPM) and you want to maintain a velocity of 8 feet per second (ft/s) to prevent noise and erosion.
- Convert Units: The formula requires consistent units. We often convert GPM to cubic feet per second (cfs).
1 GPM ≈ 0.002228 cfs.
100 GPM × 0.002228 = 0.2228 cfs.
- Calculate Area: A = Q / v
A = 0.2228 / 8 = 0.02785 square feet.
- Calculate Diameter (in feet): d = √ [ (4 × 0.02785) / 3.14159 ] ≈ 0.188 feet.
- Convert to Inches: 0.188 ft × 12 inches/ft ≈ 2.26 inches.
In this scenario, a pipe with an inner diameter of exactly 2.26 inches is required. Since 2.26 inches is not a standard size, you would typically select a 2.5-inch or 3-inch nominal pipe size, depending on the schedule (wall thickness) of the pipe.
Why Velocity Matters
Choosing the velocity variable is the most critical part of this calculation. Standard engineering practices suggest different velocities for different applications:
- General Water Service: 4 to 10 ft/s
- Pump Suction: 4 to 7 ft/s (lower velocity prevents cavitation)
- Pump Discharge: 6 to 12 ft/s
- Drainage (Gravity Flow): 2 to 3 ft/s (ensures solids move with liquid)
Using the calculator above ensures you can quickly verify if your pipe sizing meets these critical velocity constraints.
function calculatePipeSize() {
// Get input values using var
var flowRateGPM = document.getElementById('flowRate').value;
var velocityFPS = document.getElementById('velocity').value;
var resultBox = document.getElementById('result');
var diameterDisplay = document.getElementById('diameterResult');
var areaDisplay = document.getElementById('areaResult');
// Validate inputs
if (flowRateGPM === "" || velocityFPS === "") {
alert("Please enter both Flow Rate and Fluid Velocity.");
return;
}
var q = parseFloat(flowRateGPM);
var v = parseFloat(velocityFPS);
if (isNaN(q) || isNaN(v) || q <= 0 || v <= 0) {
alert("Please enter valid positive numbers for Flow Rate and Velocity.");
return;
}
// CALCULATION LOGIC
// Formula: d (inches) = sqrt( (0.4085 * Q_gpm) / v_fps )
// Derivation:
// 1 GPM = 0.133681 ft^3/min = 0.002228 ft^3/sec
// Q_cfs = Q_gpm * 0.002228
// Area_sqft = Q_cfs / v_fps
// Diameter_ft = sqrt( (4 * Area_sqft) / PI )
// Diameter_inches = Diameter_ft * 12
// Let's use the direct constant derived from unit conversion for precision
// d (in) = sqrt( (Q(gpm) * 0.4085) / v(ft/s) )
var constant = 0.4085;
var diameterSquared = (q * constant) / v;
var diameterInches = Math.sqrt(diameterSquared);
// Calculate cross-sectional area in square inches for additional info
var radius = diameterInches / 2;
var areaSqInches = Math.PI * (radius * radius);
// Display Results
resultBox.style.display = "block";
// formatting to 2 decimal places
diameterDisplay.innerHTML = diameterInches.toFixed(3) + '" (Inches)';
areaDisplay.innerHTML = "Cross-Sectional Area: " + areaSqInches.toFixed(3) + " sq. inches";
}